Single sheet lithographic dtr master and method of use



May 12, 1970 A, R JR, ETAL 3,511,656

SINGLE SHEET LITHOGRAPHIC DTR MASTER AND METHOD OF USE Filed Aug. 24, 1966 0 M i J Gelding layer 2011'}; 51/1/87 Hahdc l6 fbfasszum 771100 an GWCM mm 1 wmk a F m 4 mm and u 511 427 Base Sheei l5 (Phaio Nqg.)

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United States Patent Int. Cl. G03c 5/54 US. CI. 96-29 3 Claims ABSTRACTOF THE DISCLOSURE A one sheet lithographic duplicating DTR master inwhich both the silver halide negative layer and the silver receptivehydrophilic lithographic layer are present in a single base sheet withthe silver halide negative layer overlying the silver receptivelithographic layer.

This is a continuation-in-part of our copending application Ser. No.498,192, filed Mar. 31, 1955, now Pat. No. 3,278,958, and entitledMethod of llmaging a Photolithographic Plate and Elements for Use inPreparation of Same.

This invention relates to the production of multiple copies by alithographic duplicating process and it relates more particularly to themanufacture of a new and improved lithographic plate and to a new andimproved process for producing the ink receptive, water repellent imageon the lithographic surface of the plate.

Various methods are employed in the lithographic art for the formationof the ink receptive, water repellent image on a water receptive, inkrepellent surface of a lithographic duplicating plate. To the present,these processes may be divided into two principal groups generallyreferred to as the direct image process and the indirect orphotolithographic processes. In the direct process, an ink receptive,water repellent imaging material is applied directly onto thelithographic surface of the lithographic plate. For such purposes, thelithographic plate may be imaged by the use of a writing instrument forapplying the oleophilic, water repellent imaging material onto thesurface of the plate by means of a typewriter or by a die, using aribbon or a transfer sheet coated with an ink receptive, water repellentimaging material which is transferred by the impressions from thetransfer sheet to the lithographic surface to form the image thereon.

The indirect or photolithographic process is used for the reproductionof copies from an original. In general, a photographic negative is firstproduced of the original and then the negative is exposed in combinationwith a lithographic plate in which the lithographic surface has beenpresensitized with a material such as a resin-forming diazo compound orwith a bichromate capable of tanning the colloid in combinationtherewith in the exposed areas whereby the exposed areas are convertedto an ink receptive, water repellent surface upon exposure to light toform the image thereon. The light sensitive materials remaining in theunexposed portions of the plate, or the non-imaged portions must beremoved, as by washing, before use can be made of the plate to producecopies.

The concepts described and claimed herein have application chiefly tothe indirect process for the production of an imaged lithographic plateand the invention will hereinafter be described with reference to themanufacture and use of such a photolithographic plate.

Photolithographic plates of the type heretofore produced have beenconstructed chiefly with a surface sensitized with a light-sensitivematerial, such for example as a resin-forming diazo compound which isconverted to an ink receptive, water repellent resinous material uponexposure to light. Such photolithographic plates formed withlight-sensitive diazo compounds are subject to dark or thermaldecomposition reactions which results in overall ink receptivity orscumming. As a result they have limited shelf life and it is necessaryto prescribe an expiration period of relatively short time in which theplate must be used.

Aside from the limited shelf life inherent in plates of the typeheretofore produced, the labor and equipment required for thepreparation of a photolithographic plate to produce the image thereonfrom an original are excessive and relatively expensive.

The more recently developed xerographic process for producing an imagedlithographic plate from an original embodies fewer limitations than thediazo-sensitized photolithographic plates, especially from thestandpoint of plate life and the character of the original, but theinitial investment in equipment required is excessive and the methodsfor preparing the masters are tedious and involved.

It is an object of this invention to produce a new and improvedlithographic plate and method for imaging same which is not subject toany of the deficiencies and disadvantages of the processes and productsheretofore employed.

More specifically, it is an object of this invention to produce a newand improved lithographic plate and process for imaging same and it is arelated object to produce a lithographic plate of the type describedwhich can be fabricated in a simple and eflicient manner; which isproduced of low cost and readily available materials; in which theprocess enjoys the desired degree of exposure latitude; in which theprocess has a broad range of spectral sensitivity; which does notrequire an initial investment of expensive equipment for use in imagingthe plate, which can be imaged in a simple and eflicient manner from theoriginal without an additional expenditure of time and labor; which hasapplication chiefly as a positive working photolithographic plate; whichmay be used as a direct image plate, and which can be used to produce alarge number of copies of good quality.

It is a further object of this invention to produce a lithographic plateand to provide a one-step photographic process for imaging same, and itis a related object to produce an imaged lithographic plate by aphoto-reflex process.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of the inven- 3 tion is shown in theaccompanying drawing in which- FIG. 1 is a perspective view, partiallyin section, of a photolithographic plate embodying features of theinvention of the parent application;

FIG. 2 is a schematic elevational view illustrating the arrangement ofparts in an initial step of the process;

FIG. 3 is a perspective view, partially in section, of the elementprepared by the step of FIG. 2;

FIG. 4 is a schematic sectional elevational view illustrating a finalstep in the manufacture of the imaged lithographic plate; and

FIG. 5 is a perspective view, partially in section, of thephotolithographic plate embodying the concepts of thiscontinuation-impart application.

In the Rott Pat. No. 2,352,014, description is made of a single copyprocess wherein a photographic image of an original produced in a silverhalide layer is caused to produce a reverse image on a copy sheet,provided the silver halide layer, after being exposed to light for theproduction of a master image and then being impregnated with a developerto develop the image, is pressed or squeezed in the presence of afogging agent and a silver halide solvent onto' the copy sheet while thelayer is still imbibed with the developing liquid. That part of thesilver halide in the layer which was not reduced during developmentafter exposure to light and which in the ordinary photographic processwould be fixed out of the fixing bath, will adhere to and enter the copysheet surface by diffusion and will thus produce thereon a reversedimage. In order to render this image freely visible, the light sensitivelayer containing the master image will normally be removed from the copysheet.

In the Rott process, use may be made of the silver halide solventscontained in the usual photographic developers, such as sodium sulfite,sodium thiosulfate and the like. As fogging agents, use is made ofsubstances capable of promoting the reduction of silver halides withoutrequiring the action of light, such for example as colloidal silver,colloidal forms of sulphur, silver sulfides, hypophosphites, stannouschloride, and organic compounds which are capable of splittingoff silverin the form of bivalent ions, such as thiosinamine. Such fogging agentsare preferably embodied in the copy sheet during manufacture thereof orby subsequent impregnation.

It has now been found that when use is made of an alkali metalthiocyanate, such as sodium, potassium or ammonium thiocyanate, as anintermediate for tying up the silver halide for reduction, somewhatsimilar to the fogging agents of Rott, instead of producing a reversedimage as a single copy on a receptive material or copy sheet, a reversedimage of an oleophilic or water repellent image is formed which, whenproduced on a hydrophilic, water receptive lithographic surface, can beused to produce a large number of inked copies by conventionallithographic printing methods.

While the reversed image of the oleophilic, water repellent or inkreceptive imaging material is formed by diffusion on the lithographicsurface as a reaction product when the alkali metal thiocyanate ispresent as an ingredient dissolved in the development solution, it ispreferred to supply the alkali metal thiocyanate as a substantiallycontinuous coating on the lithographic surface of the lithographic platewhich is brought into contact with the photographic image produced inthe silver halide layer.

It is preferred to make use of a plate having anonporous, non-absorbentsurface because the amount of complexed silver halide available fortransfer from the photographic image on the exposed negative or the likeis usually insufiicient to develop the desired image intensity on thesurface of the lithographic plate when portions thereof are capable ofbeing diffused inwardly into the interior of the plate. Thus it isdesirable to make use of a plate formed of metal such as zinc oraluminum in the form of a rigid plate, sheet stock or foil which hasbeen treated on the printing surface for rendering the surfacehydrophilic, as by brushing, silicating, anodizing, etching and thelike. Instead, use can he made of a paper lithographic plate formed witha hydrophilic colloid coating such as described in plates formed inaccordance with the teaching of the US. patents of Frost No. 2,534,588,Worthen No. 2,534,650, Van Dusen No. 2,542,784, and Shepherd No.2,154,219, or parchment plates or plates formed of lithographic stone orthe like.

In preparation of the coated plate, the alkali metal thiocyanate can beapplied from solution by conventional coating means, such as by spraycoating, flow coating, brush coating, roller coating, dip coating andthe like. It will be suflicient if a monomolecular layer is formed ofthe alkali metal thiocyanate but it is preferred to provide an amountgreater than a monomolecular layer for development of maximum imageintensity. The upper limit of concentration, which depends greatly onthe structure of the film negative and the method of use, can best beestablished from a few simple trials to determine the concentration atwhich the image begins to walk off at the surface.

It has been found that the ink receptivity of the reversed image formedon the lithographic surface is markedly improved to produce inked copiesof better quality when a soluble sulfide, such as sodium sulfide,potassium sulfide or ammonium sulfide is present on the surface of thelithographic plate. The sulfide may be applied to form a coating on thelithographic surface separate and apart from the alkali metalthiocyanate but it is possible to combine the sulfide with thethiocyanate for application together to form the desired coating on thehydrophilic lithographic surface.

For the development of the improved characteristics by the sulfide, itis desirable to make use of the sulfide in amounts ranging from 1 partby weight thereof to 1-5 parts by weight of the thiocyanate or similaragent reactive to form the insoluble, oleophilic reaction product. Whenthe ratio of sulfide to thiocyanate or other suitable fogging agent isgreater than 1 to 1, the printing plate may be less satisfactory fromthe standpoint of ink receptivity in the imaged areas. When the ratio ofsulfide to thiocyanate is less than 1 to 5, the printing plate becomesless satisfactory from the standpoint of scumming and reduced visibilityof the image formed on the plate believed to form by reaction of thesulfide with silver to form a dark silver sulfide reaction product inthe imaged areas of the plate.

In the practice of this invention, it is preferred to make use of thesulfide in the ratio of about 1 part by weight sulfide to 3 parts byweight thiocyanate or the like. Instead of sodium sulfide, use can bemade of other soluble sulfides such as potassium sulfide and ammoniumsul fide, as previously described, or water soluble compounds capable ofreleasing sulfide ions for reaction upon solu tion in the transfermedium.

By way of still further improvement, it has been found that the inkreceptivity of the reversed image and the anchorage of the oleophilicwater-insoluble image produced on the plate surface is increased by thepresence of lead ions on the lithographic surface, preferably in theform of a soluble lead salt, such as lead acetate, or other solublebivalent metal salts such as lead chloride, lead propionate, leadnitrate and similar salts of zinc, nickel, copper, cobalt and the like.Since the lead salts form insoluble compounds with the sulfides, it isdesirable, when used, to apply the lead as a coating onto thelithographic plate separate and apart from the sulfide and thiocyanate.The concentration of metal salts is not critical as long as sufiicientlead ions are present in the coating to cause development of the desiredoleophilic material upon diffusion of the complexed silver halide fromthe photographic image.

The following is a description of the preferred practice of thisinvention:

EXAMPLE I Manufacture of the lithographic plate For use in the practiceof this invention, an aluminum sheet 10, the surface of which has beentreated by brushing, silicating, anodizing, etching or the like, torender the surface lithographic, is coated with a solution containing 15parts by weight potassium thiocyanate and 30 parts by weight sodiumsulfide in 80 parts by weight of water. Application of the coating ismade by any conventional process, such as by spray coating, rollercoating, brush coating and the like but it is preferred to coat thetreated aluminum surfaces by means of a pair of squeegee rolls mountedto engage the opposite sides of continuous strips of aluminum advancedin face to face relation from a pair of feed rolls.

The coating composition is applied in quantities sufficient tocompletely coat the surface of the aluminum to provide at least amonomolecular layer 11. The amount applied to the surface of the plateis such that the coating air dries within a very short time, such forexample as in about -30 seconds, without the necessity for usingelevated temperatures.

While not essential, the first coating may be subsequently coated with a10 percent solution of lead acetate in water. Application is made insubstantially the same manner as the first coating to provide a thinlayer '12 following which the sheet is dried, as by air drying, in arelatively short time such as from 1030 seconds.

An aluminum sheet treated in the manner described is not sensitive tolight and thus may be manufactured in mass production processes inunlimited amounts and may be sheeted and packaged for subsequent use inthe manufacture of imaged photolithographic plates without limitation asto the conditions of storage or the length of time intervening betweenmanufacture and use.

EXAMPLE II Preparation of the imaged master Description will now be madeof the use of the lithographic plate of Example I in the preparation ofan imaged master by print-through contact exposure from an original 14.First a photo-negative containing a light sensitive silver halide in agelatin emulsion or the like hydrophilic colloid coating 16 on asuitable base sheet such as paper or plastic film stock is exposed to anoriginal by reflex or by print-through contact or by projection printingto form a latent image in the silver halide gelatin emulsion. It ispreferred in this process to make use of a photographic negative whichis transparent or translucent in order to give maximum latitude of theoriginal. The photographic negative does not have to be flexible and thethickness and dimension of the negative do not constitute importantfactors in the process. By way of example, a suitable photographicnegative is marketed by Agfa under the trade name Copyrapid.

The exposed photographic negative is developed in a solution containingthe normal developing components plus a material which is a solvent forthe silver halide such as in a typical monobath developer including adeveloper and fixer such as are ordinarily employed in photographicpractice, a typical composition of which may be formulated of gramshydroquinone, 30 grams sodium hydroxide, grams sodium sulfite, 10 gramssodium thiosulfate, 1.5 grams benzotriazole, with water sufficient tomake up one liter. This development is carried out under such conditionsthat the photographic negative wet with the solution and thephotolithographic surface wet with the solution are brought into surfacecontact with each other, as illustrated in FIG. 4, so that the solublesilver complex that is formed of the silver halide in the photographicimage is caused to diffuse to the corresponding areas of thelithographic surface. Usually, con- 6 tact under the conditionsdescribed for from /2 to 2 minutes is sufiicient to elfect the desiredtransfer for the development of the reversed, oleophilic,water-insoluble image on the lithographic plate.

The lithographic surface containing the alkali metal thiocyanate aloneor in combination with sodium sulfide and/or lead acetate promotes thereduction of the silver halide complex without the action of light toproduce an oleophilic, water-insoluble reaction product which istransferred or forms on the surface of the lithographic plate. Theoleophilic reaction product formed in the areas corresponding to theoriginal becomes strongly anchored to the lithographic surface to formthe image which can now be used to produce a large number of copies bylithographic duplicating technique. The printing plate may be lacqueredby known techniques or printed without lacquer, as preferred, on anoffset lithographic press to produce exact and clear copies of theoriginal.

Instead of making use of an alkali metal thiocyanate, a Water-insoluble,oleophilic reversed image having some degree of ink receptivity may besecured by the use of a system based on the use of argyrol, a silverprotein and lead salts but the ink receptivity and the intensity of thecopy that is produced is not as good as that secured with a system basedupon the use of an alkali metal thiocyanate alone or in combination witha soluble sulfide or combinations thereof with soluble lead salts. Awaterinsoluble, oleophilic reversed image can also be secured when thelithographic surface is coated with dithioxamide and a lead salt, withor without a soluble sulfide such as lead sulfide. Lead and iron saltsin combination with a soluble sulfide applied independently to formseparate layers show some degree of ink receptivity. These other systemsmay be used in the production of a lithographic plate in accordance withthe procedures of Examples I and II by substitution of the solutions ofthe above materials for the thiocyanate and sulfide and for the leadacetate. In the presence of lead acetate or other soluble bivalent metalsalts of the type described, with or without a soluble sulfide, almostany of the fogging agents of the type described in the Rott patent whichwill precipitate soluble silver may be used to produce an-ink receptive,water repellent, reversed image on a lithographic surface for use in theproduction of multiple copies.

The following are further examples of compositions which may be used inthe practice of this invention in lieu of the first coating compositionof Example I:

EXAMPLE III Parts by weight Sodium thiocyanate 10 Water 90 EXAMPLE IVDithioxamide l0 Ammonium sulfide 5 Water 85 EXAMPLE V Lead acetate 10Thiosinamine 10 Water EXAMPLE VI Argyrol-silver caseinate 15 Water Thefollowing compositions may be employed in lieu of the lead acetatesolution applied as a second coating on the surface of the lithographicplate:

EXAMPLE VII Percent by weight Barium chloride in water -15 EXAMPLE VIIICopper acetate in water 5-20 EXAMPLE IX Zinc chloride in water 5-20Where the sulfide or its equivalent is omitted from the first coating,the polyvalent metal salt may be formulated into a single coatingcomposition with the cyanate for application onto the lithographicsurface as illustrated by the composition of the following example:

EXAMPLE X Percent by weight Ammonium thiocyanate 3-20 Zinc chloride 5-15Remainder water.

A plate formed of compositions of Examples III, IV, V and VI, forexample, may be employed without the top coating with compositions ofExamples VII, VIII and IX, but plates formed of compositions ofExamples'III and IV are improved by the applications of compositions ofExamples VII, VIII and IX to form top coatings.

Instead of making use of a photo-negative, it has been found that thegelatin coating sensitized with the silver halide may be applied as acoating directly onto the surface of a lithographic plate which haspreviously been coated with the desired materials for reaction toproduce a desirable silver compound with the silver halide. Afterexposure, the silver halide in the unexposed areas corresponding to theimage in the original is caused to diffuse to the coated surface of thelithographic plate during immersion in the developer for the exposedsilver halide in which a suitable solvent for the unexposed silverhalide complex is present to enable diffusion.

Transfer of the silver halide in the processes described has been foundto cause adhesion of the lead salts and the formed reaction product withthe silver salts to the aluminum or other base of the lithographicplate. Upon formation of the water insoluble, oleophilic image as areaction product, the gelatin is removed from the surface with warmwater.

This continuation-in-part application is addressed to the aforementionedsingle sheet photolithographic master which embodies the negative in theform of a silver halide stratum 100 is a part of and superimposed on thewater receptive, ink repellent, water-insoluble, lithographic, silverreceptive stratum 102 containing the nuclei or fogging agent forprecipitation of soluble silver halide diffused from the unexposedportions of the silver halide stratum 100 to produce an ink receptive,water repellent, silver image on the lithographic surface.

To the point of the application of the silver halide stratum 100, whichfunctions as the negative, the construction of the photo-lithographicplate is the same as that which has previously been described withreference to a photo-lithographic plate for use with a separate silverhalide negative. For the manufacture of a composite plate, the silverhalide stratum 100 is applied directly onto the lithographic surface 102of the base sheet 104 of paper, aluminum foil, or the like.

For this purpose, application is made of an aqueous solution formulatedto contain 3-10 percent by weight of gelatin dissolved therein andsilver chloride in the ratio of one part by weight silver chloride to5-10 parts by weight of gelatin, with a small amount of formaldehyde(0.1-2 percent by weight) and saponin (0:01-01 percent by Weight), thelatter of which are incorporated for purposes of stabilization of thecoating composition. The composition for the negative stratum is appliedto form a thin coating on the lithographic surface, such as in a coatingweight of from 2-10 pounds per 3,000 square feet of surface area, andthereafter the coating is dried.

In use, the single sheet master is exposed in the normal manner to theimage.

Development is made in the normal manner by immersion or by wetting thesurface with a liquid developing composition of the type previouslydescribed formulated of an aqueous alkaline solution containing a silverhalide developer and a silver halide solvent whereby the silver halide,in the exposed areas of the silver halide stratum 100, is reduced tosilver while silver halide in the unexposed areas is dissolved anddiffused, as a soluble complex, to the underlying lithographic surface,identified as the silver receptive stratum 102 where the silver halidecomplex is reduced in the presence of the nucleating agent to a silver,ink receptive, water repellent image which becomes strongly bonded tothe underlying lithographic surface, as described in the combinationwhich makes use of a separate silver halide stratum.

After development, the silver halide stratum is removed by washing or byswabbing with water, preferably warm water, to expose the underlyinglithographic surface having the silver, ink receptive image anchoredonto the surfaces thereof.

Thereafter, the imaged plate can be mounted on a conventionallithographic press for alternate wetting with aqueous repellent andoleaginous ink composition with intermediate contact with dry copysheets to produce multiple copies.

In sheeting, the plate may be formed to size with suitable openings inthe leading edges for attachment to the hooks provided on the platecylinder of a lithographic press, and the plates may also be formed withserrated trailing edges for engagement by the clamping means on theplate cylinder.

It will be understood that the concepts of this invention are notdependent on the concentrations of the various materials in the coatingcompositions so long as a uniform coating can be applied to the surfaceof the plate for deposition of a thin layer of the essential ingredientsthereon. It would be undesirable to make use of coating compositionshaving high concentrations of the salts or other materials such as inexcess of 30 percent by weight, since such large amounts are unnecessaryand such coating compositions might render the product and processuneconomical.

It will be understood that changes may be made in the details ofconstruction of the plate, formulation of the coating compositions, andthe method of application, and that changes may be made in the manner ofuse of the plate without departing from the spirit of the invention,especially as defined in the following claims.

We claim:

1. A multiple copy process comprising the steps of photo-exposing alithographic duplicating master comprising a base sheet, a silverreceptive stratum containing nuclei for precipitation of silver from awater soluble silver complex and in which the surface of the silverreceptive stratum is hydrophilic, water receptive, water insoluble andink repellent, and a silver halide stratum on the surface of andintegral with the silver receptive stratum, applying aqueous alkalinesolution of a silver halide developer and a silver halide solvent to thephotoexposed silver halide stratum atop the silver receptive stratum,reducing the exposed silver halide in the silver halide stratum tosilver and diffusing unreduced silver halide or complex formed thereoffrom the unexposed areas of the silver halide stratum to the underlyingsilver receptive stratum to produce from the unreduced silver halide orcomplex in conjunction with the nuclei a visible image on the silverreceptive stratum in which the image is characterized as an oleophilic,ink receptive material, wetting the imaged silver receptive stratum withaqueous medium to wet out the non-imaged areas, coating the silverreceptive stratum with an ink which preferably Wets out the imagedareas, and pressing the inked surface onto copy sheets for the transferof the ink image thereto.

2. A multiple copy process as claimed in claim 1 which includes thesteps of repeatedly wetting and inking the imaged surface in successiveapplications with pressing 15 References Cited UNITED STATES PATENTSv2,843,485 7/1958 Yutzy et a1. 96-76 2,878,121 3/1959 Gray 96291,742,710 1/1930 Krebs 9629 2,352,014 6/1944 Rott 9629 2,698,237 12/1954Land 9629 2,698,245 12/1954 Land 9629 2,774,667 12/ 1956 Land et a1 96292,774,668 12/1956 Rodgers 9676 3,220,837 11/1965 Land et a1. 9629FOREIGN PATENTS 440,736 1/ 1936 Great Britain.

NORMAN G. TORCHIN, Primary Examiner I. R. HIGHTOWER, Assistant ExaminerUS. Cl. X.R.

development by treatment of the surface with warm Water. 20 9633, 76

